Social integration, daily social interaction, and health risk pathways in midlife a consistent body of evidence, from experimental rodent models to human epidemiological studies, suggests that chronic interpersonal stress may be associated with increases in systemic inflammation, which is a risk factor for early morbidity and mortality i midlife. In order to better understand these effects and potentially address them, we need to better characterize the specific social behaviors that may trigger inflammatory responses. In the rodent research, recurrent aggressive interactions with conspecifics appear to elicit systemic changes in inflammation. Similarly, laboratory evidence in humans suggests that conflictual marital interactions, especially those that are accompanied by hostile behaviors, are associated with increased concentration of circulating inflammatory markers. Little is known, however, about whether similar social behaviors may trigger inflammatory responding in the course of daily human interaction, and the extent to which these effects may account for observed associations between chronic interpersonal stress and inflammation. As part of an ongoing investigation of social relationships and health risk pathways in midlife (R01 AG041778), we are collecting observations of social interactions, mood, and inflammation, among other variables. This revision proposal adds 4 additional measures to this parent study; interview assessments of life stress; measures of glucocorticoid receptor (GCR) sensitivity; urinary catecholamines; and daily blood spot measures of interleukin-6 (IL-6), an inflammatory marker. With these additions, this study provides us with a unique opportunity to examine the social processes that may trigger inflammatory activity during everyday life, and to explore some of the mechanisms that may explain these effects. Understanding how daily social interactions may explain some of the effects of chronic interpersonal stress on health is of critical importance for developing appropriate treatment targets and methods of intervention in this area.